Factor VII is a plasma serine protease involved in the initiation of the coagulation cascade. It is present in human blood at a concentration of approximately 500 ng/mL, with about 1% of the total amount in the proteolytically active form factor VIIa (Morrissey, J. H. et al. Blood 1993, 81, 734-744). Factor VIIa binds with high affinity to its cofactor, tissue factor, in the presence of calcium ions to form a complex with enhanced proteolytic activity (Carson, S. D. and Brozna, J. P. Blood Coag. Fibrinol. 1993, 4, 281-292). Tissue factor is normally expressed in cells surrounding the vasculature, and is exposed to factor VIIa in blood by vessel injury or atherosclerotic plaque rupture. Once formed, the tissue factor/factor VIIa complex initiates blood coagulation by proteolytic cleavage of factor X to factor Xa, factor IX to factor IXa and autoactivation of additional factor VII to VIIa. Factor Xa, generated either directly by tissue factor/factor VIIa or indirectly through action of factor IXa, catalyzes the conversion of prothrombin to thrombin. Thrombin converts fibrinogen to fibrin, which polymerizes to form the structural framework of a blood clot, and activates platelets, which are a key cellular component of coagulation (Hoffman, M. Blood Reviews 2003, 17, S1-S5). In addition, there is evidence that tissue factor is present in blood, likely in an encrypted form that is de-encrypted during clot formation. (Giesen, P. L. A. et al. Proc. Natl. Acad. Sci. 1999, 96, 2311-2315; Himber, J. et al. J. Thromb. Haemost. 2003, 1, 889-895). The tissue factor/factor VIIa complex derived from blood borne tissue factor may play an important role in propagation of the coagulation cascade (clot growth) and in thrombus formation in the absence of vessel wall injury (i.e., stasis induced deep vein thrombosis or sepsis). The source of blood borne tissue factor is an area of active research (Morrissey, J. H. J. Thromb. Haemost. 2003, 1, 878-880).
While blood coagulation is essential to the regulation of an organism's hemostasis, it is also involved in many pathological conditions. In thrombosis, a blood clot, or thrombus, may form and obstruct circulation locally, causing ischemia and organ damage. Alternatively, in a process known as embolism, the clot may dislodge and subsequently become trapped in a distal vessel, where it again causes ischemia and organ damage. Diseases arising from pathological thrombus formation are collectively referred to as thrombotic or thromboembolic disorders and include acute coronary syndrome, unstable angina, myocardial infarction, ischemic stroke, deep vein thrombosis, peripheral occlusive arterial disease, transient ischemic attack, and pulmonary embolism. In addition, thrombosis occurs on artificial surfaces in contact with blood, including catheters and artificial heart valves. Therefore, drugs that inhibit blood coagulation, or anticoagulants, are “pivotal agents for prevention and treatment of thromboembolic disorders” (Hirsh, J. et al. Blood 2005, 105, 453-463).
Because of its key role in the coagulation cascade, researchers have postulated that inhibition of factor VIIa could be used to treat or prevent thrombotic or thromboembolic disease. (Girard, T. J.; Nicholson, N. S. Curr. Opin. Pharmacol. 2001, 1, 159-163; Lazarus, R. A., et al. Curr. Med. Chem. 2004, 11, 2275-2290; Frederick, R. et al. Curr. Med. Chem. 2005, 12, 397-417.) Several studies have confirmed that various biological and small molecule inhibitors of factor VIIa have in vivo antithrombotic efficacy with a low bleeding liability. For instance, it has been demonstrated that a biological factor VIIa inhibitor XK1, comprising a hybrid of Factor X light chain and tissue factor pathway inhibitor first kunitz domain, prevents thrombus formation in a rat model of arterial thrombosis, with no change in bleeding time or total blood loss (Szalony, J. A. et al. J. Thrombosis and Thrombolysis 2002, 14, 113-121). In addition, small molecule active site directed factor VIIa inhibitors have demonstrated antithrombotic efficacy in animal models of arterial thrombosis (Suleymanov, O., et al. J Pharmacology and Experimental Therapeutics 2003, 306, 1115-1121; Olivero, A. G. et al. J. Biol. Chem. 2005, 280, 9160-9169; Young, W. B., et al. Bioorg. Med. Chem. Lett. 2006, 16, 2037-2041; Zbinden, K. G. et al. Bioorg. Med. Chem. 2006, 14, 5357-5369) and venous thrombosis (Szalony, J. A., et al. Thrombosis Research 2003, 112, 167-174; Arnold, C. S., et al. Thrombosis Research 2006, 117, 343-349), with little impact on bleeding time or blood loss. Moreover, the biological factor VIIa inhibitor recombinant nematode anticoagulant protein c2 (rNAPc2) is currently under clinical investigation for treatment of acute coronary syndromes. Results of initial clinical trials demonstrate that rNAPc2 prevents deep vein thrombosis in patients undergoing total knee replacement (Lee, A., et al. Circulation 2001, 104, 74-78), reduces systemic thrombin generation in patients undergoing coronary angioplasty (Moons, A. H. M. J. Am. Coll. Cardiol. 2003, 41, 2147-2153), and reduces magnitude and duration of ischemic events in patients with acute coronary syndromes (Giugliano, R. P. et al. World Congress of Cardiology 2006, Barcelona, Poster #3897).
Work has accordingly been performed to identify and optimize factor VIIa inhibitors. For example, U.S. Pat. No. 5,866,542 describes recombinant nematode anticoagulant proteins which inhibit factor VIIa. U.S. Pat. No. 5,843,442 discloses monoclonal antibodies or antibody fragments possessing factor VIIa inhibitory activity, and U.S. Pat. No. 5,023,236 presents tripeptides and tripeptide derivatives that inhibit factor VIIa.
While a number of factor VIIa inhibitors have been discussed in the art, improved inhibitors, especially non-peptide inhibitors, of serine proteases for the treatment of thromboembolic disorders are always desirable. The present invention discloses 2-(aryloxy)acetamides and analogues thereof as inhibitors of coagulation factor VIIa and, as such, their utility in the treatment of thromboembolic disorders.
In addition, it is also desirable to find new compounds with improved pharmacological characteristics compared with known serine protease inhibitors. For example, it is preferred to find new compounds with improved factor VIIa inhibitory activity and improved selectivity for factor VIIa versus other serine proteases. Also, it is preferred to find new compounds with improved activity in in vitro clotting assays, such as the prothrombin time (PT) assay. (for a description of the PT assay see, Goodnight, S. H.; Hathaway, W. E. Screening Tests of Hemostasis. Disorders of Thrombosis and Hemostasis: a clinical guide, 2nd edition, McGraw-Hill: New York, 2001 pp. 41-51). It is also desirable and preferable to find compounds with advantageous and improved characteristics in one or more of the following categories, which are given as examples and are not intended to be limiting: (a) pharmacokinetic properties, including oral bioavailability, half life, and clearance; (b) pharmaceutical properties; (c) dosage requirements; (d) factors which decrease blood concentration peak-to-trough characteristics; (e) factors that increase the concentration of active drug at the receptor; (f) factors that decrease the liability for clinical drug-drug interactions; (g) factors that decrease the potential for adverse side-effects, including selectivity versus other biological targets; and (h) factors that improve manufacturing costs or feasibility.